1. Field of the Invention
The field of this invention lies within the printer art. More specifically, it lies within the printer art pertaining to printing continuous sheets that can be printed by impact printers such as line printers, or thermal printers, or laser printers. The field is even more specifically directed toward stacking printed sheets on a continuous basis to avoid bunching of the sheets or improper formation of the paper stack after printing.
2. Description of the Prior Art
The prior art pertaining to printers and paper stackers in combination therewith, is replete with various types of printers in combination with stackers. Such stackers, stack printed paper or media on a continuous basis or as multiple forms.
One of the major problems with the prior art is that continuous media or paper is generally stacked in a container that is moved downwardly in order to accommodate an increasing amount of media or paper being stacked. This requires a substantial frame and mechanism in order to support and move a 50 pound stack of media.
Another problem of the prior art is that the driving system for the paper being stacked did not allow for a low inertia highly efficient movement of the paper, such that the printed paper emerging speed was maintained properly as the paper emanated from the printer. This is based upon the fact that the paper acceleration and deceleration during the printing process could not be properly accommodated.
Further problems with the prior art included the fact that once the paper had been delivered from the printer and was being stacked, it could not be properly stacked on a consistently closely stacked relationship at the edges.
A particular problem with regard to matrix type printers is the high rate of printing and the frequent acceleration and deceleration of paper or media by the tractor. The tractor tends to deform the tractor drive openings, holes or perforations. Included and compounded with this problem is the fan fold paper, which due to its production methods has substantial amounts of deformity even without printing thereon. This can be true even when it is unfolded and refolded again. The deformities tend to cause a paper stack that is higher on its edges than in its center.
In the prior art, it was known to move a 50 pound box of stacked paper. However, this was done on a poorly balanced overdriven basis.
Further deficiencies of the prior art were such wherein the perforation holes, or openings that were used for engagingly driving the paper, by the tractor, were not oriented such that when superimposed upon each other they allowed for stacking without curving the edges of the stack. Certain tents and bases were used to minimize the effect of the stack being piled up at a higher point due to the tractor perforation holes, or openings. However, the problem was never adequately solved and misfolds and kinks tended to occur. This in some measure was the result of the force of the tractor against the holes which caused a deformation, and raising of the edges surrounding the holes.
Other problems of the prior art were associated with the fact that the paper throat or trough leading from the printer did not properly allow for minimum movement or maximum movement within a range of printed paper emerging speeds and single form one at a time movements. Also, the stacking formation as the paper was folded downwardly was not accommodated by a positioning with a low inertia directional accommodation as the paper oscillated backwardly and forwardly during stacking.
Other drawbacks of the prior art included the fact that there were no suitable adjustable fences for accommodating various sized paper so that a combination low inertia drive and adjustable fence could maintain proper stacking over the range of various paper feed speeds.
This invention has overcome the deficiencies of the prior art by providing for a surrounding frame with a basket which rises as paper is being stacked. Pinch rollers, flexible paddles, and fore and aft fences maintain a constant height with respect to the top of the stack. This allows for maintaining an optimum geometry for each sheet of paper or media entering the stack independent of the overall stack height.
The pinch rollers comprise low inertia drive rollers that are driven by a motor shaft frictional engagement. The drive rollers are capable of rotating at a rate to accommodate maximum printed paper emerging speed therefor maintaining paper tension.
A spring loaded friction clutch surface between the drive rollers and drive shaft is accommodated by plastic bushing interfaces with rollers that do not slip on the paper. Hence there is limited wearing or relative movement against the paper by the drive rollers. Also, the low inertia drive rollers closely follow the paper's acceleration and deceleration which helps to avoid interference with the paper's normal motion during printing. The drive rollers in conjunction with idling rollers that are spring loaded against the drive rollers accommodate various paper widths and thicknesses.
As the paper falls to the top of the stack, flexible paddles in conjunction with fore and aft fences accommodate the paper so that it is driven downwardly into a neat and properly indexed stack. This stacking effect by the flexible paddles with the fore and aft fences maintains a neatly indexed stack that is contained within the general framework of the stacker which moves up as the paper is being stacked. The paddles serve to drive down the edges of the paper at the perforated fan folds for closely oriented paper overlaying at their edges.
In order to avoid mechanical imbalances, a constant force spring counterbalance is utilized to overcome the friction of the frame as it moves upwardly and downwardly. In case of a power failure, the frame stays in position without collapsing on the stack due to the constant force spring. This particular counterbalance also allows the frame to be raised and lowered manually. Furthermore, the frame can be positioned at various positions and maintained with a minimum of drive effort due to the constant balance provided by the constant force spring.
An additional feature of this invention is that the tractor perforation holes in the paper are ironed by idling rollers located at the exit of the tractors. Any deformation of the tractor perforation holes can cause increased stack height at the edges due to any hole deformation and create a concave stacked top which increases kinks and increased locking at the perforations. The idling ironing rollers of this invention help to overcome this.
The flexible paddles are provided to rotate on the paper's edge at the perforated fan folds. These help to fold the paper by pulling the paper against the fore and aft fences and compressing the stack at the edges which helps to maintain the top of the stack flat.
A paper throat or trough leading from the printer facilitates paper feeding and loading at the start of a printing job. This loading is enhanced based upon the pinch rollers that open due to the idling rollers moving from the driving rollers at an uppermost stacking position to allow loading of the paper.
The paper as it is being folded and delivered downwardly is guided through a series of guides and fences. One of the guides comprise hanging chains which tend to maintain the paper in a generally loose but slightly weighted catenary formation to allow it to stack properly.
The adjustable fore and aft fences help to contain and position the stack. This also helps in conjunction with the paddles previously mentioned to fold the paper at the fan fold edges. Both fences are coupled to one another through a cable pulley system which places the fences equidistant from the paper throat for all paper lengths from 5 to 12 inches. Attachments of the fence to the frame places paper alignment surface adjacent to the top edge of the stack allowing a short fence which can be readily moved out of the way for stack removal.
The adjustable fore and aft fences each have a set of infrared beam sensors. The infrared beam sensors are located at the paper's edge. Whenever the paper stack interrupts the beams, the frame is elevated to maintain a constant height with respect to the top of the paper stack. A time span after the sensors sense movement accommodates the paddles moving through the sensors and false movements so that movement doesn't take place until sensing occurs over an extended period of time. These beams further help to orient the frame. When it needs to be lowered, over an existing stack, the frame descends until the beam is interrupted which fundamentally means that the frame is in proper relationship to the stack. Since the sensors are attached to the fences they are placed in a fixed position relative to the edge/fold of the paper for various length paper in a coordinated manner.
In order to provide a positive movement of the travel of the paper, paddles are activated in anticipation of any frame movement and feeding of the paper. They continue to be activated for some time after initial startup to maintain the paper tension and eliminate any slack in the paper.
A paper motion detector is also utilized to determine paper movement as well as means to show whether the paper is properly moving in the paper trough or throat. In this manner, whenever paper is being printed, and there is an obstruction at the paper throat, the system declares a fault thereby stopping the printing function and avoiding data loss. A paper in detector (i.e. in the trough) assures that this fault is not declared if there is no paper in the throat area that has been printed, as is the case when printing the initial few pages of a box of paper.
From the foregoing description of the improvement over the prior art, it can be seen that this invention is substantially an advancement over the art.